Summary:
The messages for two of the warnings are misleading:
* warn_for_range_const_reference_copy suggests that the initialization
of the loop variable results in a copy. But that's not always true,
we just know that some conversion happens, potentially invoking a
constructor or conversion operator. The constructor might copy, as in
the example that lead to this message [1], but it might also not.
However, the constructed object is bound to a reference, which is
potentially misleading, so we rewrite the message to emphasize that.
We also make sure that we print the reference type into the warning
message to clarify that this warning only appears when operator*
returns a reference.
* warn_for_range_variable_always_copy suggests that a reference type
loop variable initialized from a temporary "is always a copy". But
we don't know this, the range might just return temporary objects
which aren't copies of anything. (Assuming RVO a copy constructor
might never have been called.)
The message for warn_for_range_copy is a bit repetitive: the type of a
VarDecl and its initialization Expr are the same up to cv-qualifiers,
because Sema will insert implicit casts or constructor calls to make
them match.
[1] https://bugs.llvm.org/show_bug.cgi?id=32823
Reviewers: aaron.ballman, Mordante, rtrieu
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D75613
No longer generate a diagnostic when a small trivially copyable type is
used without a reference. Before the test looked for a POD type and had no
size restriction. Since the range-based for loop is only available in
C++11 and POD types are trivially copyable in C++11 it's not required to
test for a POD type.
Since copying a large object will be expensive its size has been
restricted. 64 bytes is a common size of a cache line and if the object is
aligned the copy will be cheap. No performance impact testing has been
done.
Differential Revision: https://reviews.llvm.org/D72212
Aaron Puchert